I have the same problem with a Samsung Galaxy S3 Mini on Android 4.1
but on a Galaxy Nexus with Android 4.3 I do not see the problem and can access files directly.
Both phones are setup with MTP enabled in USB settings.

I am using Ubuntu 14.04 as well and I have the same problems with my Galaxy S3 mini (Android 4.1.2). If I plug in my phone I get an error message, that the phone can't be mounted. Then a window is opening where the internal and external storage of my phone is shown. I can browse through the folders but I can't open a file.

Rhythmbox only lists a portable player, and if I start syncing music only the internal storage of my phone is used. I can't access the external SD-card using rhythmbox.

Same problem here with Ubuntu 14.10 Utopic...
I plug in my Galaxy S4 Mini (GT-i9192) phone, or my Galaxy Note8 (GT-N5100), and I get the "Unable to mount" error... I can't open any images (JPG, PNG, etc) inside the external SD nor in the internal storage, and no thumbnail is shown for those image files.
Sometimes I get to delete files, but mostly I don't.

I can confirm the problem on Xubuntu 17.10. I think the problem is caused by braces "()" in file names. [1]
The MTP backend does not seem to like them.

It can be reproduced as follows:

1. Check that mtp works in general
2. create a regular file with only "a-z0-9" chars in a dir on your MTP device
3. mount and access it from Linux. This should work in most cases.

4. Now try the error case
5. create file with braces "()" in a dir on your MTP device.
6. mount and access it from Linux using `thunar`, `nautilus`, or even using `ls` or `cd` on the command line. This should produce the file manager (or console) to hang and no longer respond to user input, etc.

I also suspect this bug to be the cause for other bugs, e.g. in `gvfs` [2]